Combinatorial Electrochemistry: A Highly Parallel, Optical Screening Method for Discovery of Better Electrocatalysts

Abstract

Combinatorial screening of electrochemical catalysts by current-voltage methods can be unwieldy for large sample sizes. By converting the ions generated in an electrochemical half-cell reaction to a fluorescence signal, the most active compositions in a large electrode array have been identified. A fluorescent acid-base indicator was used to image high concentrations of hydrogen ions, which were generated in the electrooxidation of methanol. A 645-member electrode array containing five elements (platinum, ruthenium, osmium, iridium, and rhodium), 80 binary, 280 ternary, and 280 quaternary combinations was screened to identify the most active regions of phase space. Subsequent "zoom" screens pinpointed several very active compositions, some in ternary and quaternary regions that were bounded by rather inactive binaries. The best catalyst, platinum(44)/ruthenium(41)/osmium(10)/iridium(5) (numbers in parentheses are atomic percent), was significantly more active than platinum(50)/ruthenium(50) in a direct methanol fuel cell operating at 60 degreesC, even though the latter catalyst had about twice the surface area of the former.

Bipolar Electrodes for Rapid Screening of Electrocatalysts

“…16,17 One of the first approaches for screening electrocatalysts involved monitoring methanol oxidation using pH-sensitive fluorescent indicators. 18 An alternative method requires an array of individually addressable electrodes configured in such a way that the currents passing through the electrodes can be monitored simultaneously. 19−22 This method is effective but requires rather sophisticated microfabrication and electronics.…”

“…16,17 One of the first approaches for screening electrocatalysts involved monitoring methanol oxidation using pH-sensitive fluorescent indicators. 18 An alternative method requires an array of individually addressable electrodes …”

Inkjet Printing Meets Electrochemical Energy Conversion

“…Each jetted ink droplet has a known composition and by controlling the number of droplets from the different inks, arrays of catalyst spots with gradient compositions can easily be prepared. After post-processing, the catalytically most active composition can be identified by using different screening methods including fluorescence, [17] employing electrode arrays, [18,19] scanning electrochemical microscopy [20,21] and electrochemical scanning droplet cells. [22] Inkjet printed electrocatalyst libraries were reported first by Reddington et al who printed Pt, Ru, Os and Ir based halide salts.…”

“…[22] Inkjet printed electrocatalyst libraries were reported first by Reddington et al who printed Pt, Ru, Os and Ir based halide salts. [17] Subsequently, quaternary PtRu-Os-Ir compositions were synthesized by chemical reduction with borohydride. A significant increase in catalytic activity was found as anode catalyst in direct methanol fuel cells by the addition of small amounts of Os and Ir, a result that was obtained thanks to the high-throughput fabrication by inkjet printing.…”

Parallel Solution Combustion Synthesis for Combinatorial Materials Studies

“…Among them, sol-gel, coprecipitation, and hydrothermal synthesis have been successfully applied to combinatorial studies of catalyst, zeolite, etc. [6][7][8][9][10] The solution combustion (SC) method is an important wet chemical synthesis technique which was first proposed by J. J. Kingsley and K. C. Patil in 1988. 11 This method has the advantage of instantaneous high temperature.…”